Energy and Power Engineering, 2013, 5, 1387-1392
doi:10.4236/epe.2013.54B263 Published Online July 2013 (http://www.scirp.org/journal/epe)
Performance Analysis of Induced Draft Fan Driven by
Steam Turbine for 1000 MW Power Units
Jianling Deng, Feifei Liang, Yang Ding, Zhiping Yang, Gang Xu, Jizhen Liu
National thermal power engineering technology research center, North China Electric Power University, Beijing, China
Received March, 2013
ABSTRACT
Boiler fan is the main power consumption device in thermal power units and the induced draft fan accounted for the
largest proportion. Reducing the energy consumption rate of induced draft fan is the main path to reduce the power
consumption rate of thermal power units. The induce fan driven by small turbine is greatly effective for reducing the
power consumption rate and the supply coal consumption rate in large thermal power plant. Take 1000 MW power units
for example, the selection of steam source for steam turbine were discussed and economic performance of the unit un-
der different steam source was compared in this paper. The result shows that compared with the motor driven method,
there is about 1.6 g/kWh decrease in supply coal consumption rate driven by the fourth stage extraction steam; whereas
there is about 2.5 g/kWh decrease in supply coal consumption rate driven by the fifth stage extraction steam.
Keywords: Induced Draft Fan; Source Steam; Auxiliary Power Ratio ; Supply Coal Consumption Rate; Investment
Recovery Period
1. Introduction
Auxiliary power ratio is a crucial indicator to the evalua-
tion of thermal power unit, it directly affects the supply
coal consumption rate of the power unit. Boiler fan plays
an important role in fossil-fired power unit’s auxiliary
power consumption and it occupies about 40% of total
auxiliary power consumption, among which induced
draft fan (ID fan) consumes approximately 20% (15% for
primary air fan, and the rest 5% for blower). Generally,
fan operation and regulation could be achieved by ad-
justing baffle or the rotation angle of diverter guide blade,
which in turn results in massive power consumption be-
cause of throttling loss. Therefore, in order to improve
system efficiency as well as reduce energy consumption,
energy-saving retrofitting of fan has been one o f the most
plausible methods to reduce energy consumption of
power plant recently [1-3].
Currently there are several ways to reduce power con-
sumption rate of fan, including replace the old fan with
high efficiency and energy-saving one (which means to
modify the old fan), speed regulation reform, operation
optimization and so on. With regard to speed regulation
reform, we can either add fluid coupling or frequency
converter. Usually frequency converter has better per-
formance than fluid coupling, but it requires high in-
vestment [4-8]. Operation optimization means when boi-
ler works normally, the booster fan is in chain spare state.
If boiler malfunctions, the booster fan automatically
starts operating, significantly mitigating its own steam
consumption.
As the largest power consumption device in all kinds
of fans, it is imperative to modify ID fan into energy-
saving type. Referring to the operating mode that replac-
ing motor-driven feed pump with steam-driven feed
pump, ID fan driven by small turbine is the major ap-
proach to reduce unit auxiliary power ratio [9]. This pa-
per gives feasibility analysis of small turbine driven by
the fourth stage extraction steam or the fifth stage extrac-
tion steam, compares the energy-saving benefit of these
two different schemes, then accumulates each scheme’s
dynamic investment recovery life based on dynamic in-
vestment recovery period theory, during which the valid-
ity calculation of each scheme is verified.
2. 1000 MW Unit Induced Draft Fan Profile
The 1000 MW unit is equipped with two axial static
blade adjustable ID fan, constructed by Chengdu power
machinery factory. They are horizontal symmetry ar-
ranged, open layout and in parallel operation. Fan model
is AN42e6(V19+4˚), it adopts imported static blade reg-
ulation, with a blade adjusting range of -75℃～＋30˚
(corresponding open feedback indication is 0～100%).
Motor type: YKK1120-10, manufactured by Xiangtan
motor, rated power is 8000 KW, power factor is 0.87,
and rated speed is 596 r/min. Table 1 and Table 2 pre-

J. L. DENG ET AL.
1388
sent operating parameters of ID fan driven by motor and
small turbine respectively.
Comparing fan efficiency in Table 1 and Table 2, it
can be found that when ID fan is driven by motor, its
efficiency decreases as working load drops, while effi-
ciency of ID fan driven by small turbine remains constant
in high efficiency area. This is attributed to the fact that
when driven by motor, the efficiency curve of ID fan
keeps unchanged on account of throttling governing, as
the flow rate decreases, its efficiency also drops. While
ID fan driven by small turbine, due to variable-speed
regulation, ID fan’s efficiency curve will change accord-
ingly if rotational speed changes, which assures that the
ID fan always operates in high efficiency area.
Table 1 and Table 2 also shows that when driven by
small turbine, ID fan’s shaft power is lower compared to
that driven by motor at constant speed, which happens in
each working condition. Thus, the lower the working
load, the larger th e reduction.
3. Steam Source Selection and Economic
Analysis of ID Fan Driven by Small
Turbine
3.1. Steam Source Selection
In principle, each stage extraction steam from main tur-
bine could be the steam source that drives the ID fan.
However, there are some drawbacks if the extraction
point is selected before intermediate reheat point: on the
one hand, efficiency will drop because steam expansion
is at excessive high temperature; on the other hand, water
erosion of last stage will be aggravated. Moreover, due to
the high pressure of supply steam, inlet steam volume
flow of the small turb ine decreases, accounting for height
reductio n of flow path no zzle and blad e.
To make up the shortages mentioned above, steam that
drives the small turbine ought to be extracted from some
stage behind intermediate reheat point, in order to reduce
final stage steam loss, it is suggested that supply steam
pressure be as low as possible. In addition, low extraction
steam pressure increases admission volume and improves
relative internal efficiency of small turbine, which will
further decrease heat consumption rate. Nevertheless, it
has to be noted that too low-pressure steam will lead to
exhaust area’s excessive enlargement of small turbine’s
last stage and restrict rotational speed improvement. Be-
sides, bigger leaving velocity loss is highly possible,
which may cause relative internal efficiency reduction.
So crossover pipe between intermediate pressure and low
pressure cylinders of main steam turbine and extraction
steam from preceding stage are favorable steam sources
for small turbine.
Based on existed conditions, available steam sources
are the third, the fourth and the fifth stage extraction
steams. In the following section, we only discuss the fea-
sibility of ID fan driven by the fourth and the fifth stage
extraction steam, because high parameters of the third
stage extraction steam have strong negative effects.
In this paper, the small turbine adopts condensing
steam type, its start and backup steams can either come
from adjacent engine or auxiliary steam generated by
startup boiler room, under normal working condition.
The fourth or the fifth stage extraction steam will be used
as steam source, there is no need to apply high pressure
steam under low working load as supply steam alone can
perfectly meets the requirement, auxiliary steam comes
from auxiliary steam main pipe of adjoining engine, for
each small turbine, an exclusive condenser is deployed,
the condenser is cooled down by circulated water, being
pressure boosted by the condensing water pump comes
with the condenser, th en the water is pumped into the hot
well located at main condenser.
Table 1. Operating parameters of ID fan when driven by motor.
Working condition
parameter BMCR THA 75%THA 50%THA 40%THA
Inlet flow rate/(m3/s) 686 648 500 357 292
Fan total pressure/Pa 6050 5651 4225 3154 2543
Fan efficiency/% 86.7 83.1 73.1 54.6 43.3
Fan working speed/(r/min) 595 595 595 595 595
Fan shaft power/kW 4787 4407 2890 2063 1715
Table 2. Operating parameters of ID fan when driven by small turbine.
Working condition
parameter BMCR THA 75%THA 50%THA 40%THA
Inlet flow rate/(m3/s) 686 648 500 357 292
Fan total pressure/Pa 6050 5651 4225 3154 2543
Fan efficiency/% 86.7 85.9 85.8 85.8 85.9
Fan working speed/(r/min) 595 562 434 310 253
Fan shaft power/kW 4787 4263 2462 1312 864

J. L. DENG ET AL. 1389
3.2. Economic Analysis
In this paper, ID fan driven by small turbine scheme is
selected on the ground of variable working condition
theory of thermodynamic system [10], with given data
such as flow rate of each stage extraction steam from the
main turbine, flow rate and parameters of feed water,
turbine exhaust steam parameters. Besides, this paper
conducts some important thermal economic indicators
under two different schemes, including heat consumption
rate, power generation coal consumption rate and supply
coal consumption rate.
3.2.1. Variable Working Condition Theory of
Thermodynamic System
During the calculation process of thermodynamic system
under variable working conditions, group of stages is
served as the calculation unit, and it is categorized by
extraction point. The first group of stages covers from
high pressure cylinder inlet to the first extraction point,
then each two extraction points make one group of stages,
the last extraction point to the final stage also make one
group of stages.
In the following equation (1), flow rate of each group
of stages is presented:
01
2
3
4
5
6
7
8
I
II I
III II
IV III
VIV
VI V
VII VI
VIII VII
DDD
DDD
DDD
DDD
DDD
DDD
DDD
DDD














(1)
where
I
D to VIII stand for pass flow rate of each unit,
0 is main steam flow rate, and 1 to are flow
rates of corresponding stage extraction steam.
D
DD 8 D
If flow rate changes, pressures before and behind each
group of stages will change, their relationship could be
obtained by Friu Geer formula as follow:
22 1,0
112
22
1,0 1 1,0 2,0
T
Dpp
DT pp

 (2)
Since temperature correction term 1,0 1 T almost
equals to 1, it’s negligible in practical calculations,
T
21
is very small, 2 and 2,0 can be ignored
because they have little effect on the result, so equation
(2) can be simplified as:
pp p p
11
1,0 1,0
Dp
Dp
 (3)
Then the extraction steam pressure is gained by the
following equation:
1
11,0
1,0
D
pp
D
 (4)
where 1: pressure before the group of stages after
working condition is changed; 1,0 : pressure before the
group of stages when working condition has not changed;
1: flow rate of the group of stages after working cond i-
tion is changed; 1,0 : flow rate of the group of stages
when working condition has not switched.
pp
DD
Assuming relative internal efficiency of the group of
stages remains unchanged, new extraction steam en-
thalpy can be approximated based on linear relation on
steam expansion line as pressure before the group of
stages (i.e extraction steam pressure) varies, specific
equation is:
1,0 2
21,0 1,02,0
1,0 2,0
(
pp
hhh h
pp

 
)
(5)
In equation (5), variables with sub 1, 2 represent data
before and behind the group of stages, while variables
with sub 0 are values when working condition has not
changed.
Pressure loss of every extraction steam pipe is deter-
mined by formula (6):
,0 ,0
i
ii
i
D
pp
D
 (6)
where i
p

and i p

are pressure loss of the i’th extrac-
tion steam before and after working condition changes
respectively, ,0i: flow rate of the i’th extraction steam
in the first place, i: flow rate of the i’th extraction
steam when working condition changes.
DD
In the following discussion, exhausted water parame-
ters of the heater are acquired provided the assumption
that terminal temperature difference and hydrophobic
end error keep unchanged in all working condition.
3.2.2. Result and An al y si s
In contrast, Changes of economic indicators of unit dri-
ven by small turbine are listed in Table 4:
It is demonstrated in Table 4 that when ID fan driven
by small turbine instead of motor, the standard coal
consumption rate increases, but auxiliary power ratio
and supply standard coal consumption are decreasing.
When adopting the fourth stage extraction steam as the
steam source, power generation standard coal consump-
tion increases by about 3 g/KWh, auxiliary power ratio
has a reduction by 1.5%, and supply standard coal con-
sumption also reduces by about 1.6 g/KWh; Whereas if
the fifth stage extraction steam is applied, there is about
2 g/KWh increase in generation standard coal consump-
tion, supply standard coal consumption has about 2
g/KWh cut down. So compared to the fourth stage ex-

J. L. DENG ET AL.
1390
traction steam scheme, the fifth stage extraction steam
scheme has an obvious reduction in supply coal con-
sumption but requires less standard coal to realize the
same power output, which means it has better economic
performance.
Table 5 shows inlet flow rate of small turbine under
tw n using the fifth stage extrac-
tio
Table 3. Economic indicators of Unit of three driven methods.
Power genera tion standard coal Auxiliary power Supply standard coal
o steam source methods.
Table 5 implies that whe
n steam as steam source, to a rather small extent, the
inlet flow rate of small turbine will increase, for example,
under BMCR working condition; only 25.69t steam is
required per hour, so it is completely feasible to use the
fifth stage extraction steam as the steam source of small
turbine.
Figures 1, 2 and 3 respectively presents comparison of
coal consumption rate, auxiliary power ratio and supply
coal consumption rate under three schemes when ID fan
driven by small turbine, althou gh there is a mild increase
in unit coal consumption rate, both auxiliary power ratio
and supply standard coal consumption rate are decreasing.
Besides, if the fifth stage extraction steam is selected as
the steam source of small turbine, more standard coal
could be saved realizing the same power output, with
better energy efficiency.
consumption/(g/kWh) ratio/% consumption/(g/kWh)
Working
scheme1 scheme2 scheme 3 scheme1 scheme2 scheme3 scheme1 scheme2 scheme3
condition
BMCR 272.20 274.96 274.13 4.22 2.72 2.72 284.20 282.65 281.79
THA 272.50 275.47 274.80 4.22 2.60 2.60 284.50 282.82 282.14
75%THA 276.61 278.97 278.15 4.50 3.14 3.14 289.64 288.02 287.17
50%THA 286.17 289.34 288.46 4.70 3.08 3.08 300.28 298.53 297.63
40%THA 297.89 301.32 300.15 4.90 3.31 3.31 313.24 311.64 310.43
Table 4. Changes of economic indicators of Unit driven by small turbine.
Working condition
Indicator/unit BMCR THA 50%THA 40%THA 75%THA
Power generation standard +2.76 +1.93+2.97 +2.30+2.36 +1.54+3.17 +2.29 +3.43 +2.26
coal consumption/(g/kWh)
Auxiliary power ratio/% -1.50 -1.50 -1.62 -1.62 -1.36 -1.36 -1.62 -1.62 -1.59 -1.59
supply standard coal -1.55 -2.41 -1.68 -2.36 -1.62 -2.47 -1.75 -2.65 -1.60 -2.81
consumption/(g/kWh)
notes on the left side refer to changes of economic indicators of unit driven by small turbine when the fourth stage extraction steam is
Table 5. Inlet flow rate of small turbine under two steam source methods.
Working Inlet flow rate of small turbine
extr/)
Inlet flow rate of small turbine
wh Difference(the fifth stage
fo
: in the table above, figure
applied, while the right side refer to the fifth stage extraction steam.
condition when using the fourth stage
athction steam as steam source/(en using the fifth stage extraction steam as steam source /(t/h) extraction steam minus the urth stage extraction steam）
BMCR 21.88 25.69 3.81
THA 19.81 23.30 3.49
75%THA 12.30 17.08 4.78
50%THA 6.47 9.90 3.43
40%THA 4.36 5.39 1.03

J. L. DENG ET AL. 1391
Figure 1. Comparison of coal consumption r ate under three
schemes.
Figure 2. Comparison of auxiliary power ratio before/after
reformation.
Figure 3. Comparison of supply c oal consum ption rate under
three schemes.
4. Conclusions
Based on variable working condition theory of thermo-
ven by small turbine of 1000 MW
several alternative steam sources for
B01),
unds for the Central Univer
e International Science and
,
Vol. 5, 2008, pp
[2] J. H. Wu, “Enm of Boiler Fans in
Analysis of Boiler Fans in Pow-
n the Reduction of the Station
sis on Benefit after Transmission of
ng and H. P. Wang, “Applications of High
dynamic system, this paper presents techno-economic
analysis of ID fan dri
unit, then discusses
the small turbine, with a comparison between two dif-
ferent schemes. Results show that when adopting the
fifth stage extraction steam as steam source instead of the
fourth stage extraction steam, there exists an obvious
reduction in supply coal consumption rate with shorter
investment recovery period and more economic benefits.
Either the fourth stage extraction steam or the fifth stage
extraction steam is selected as the steam source; maxi-
mum investment recovery period is within three years.
Noting that auxiliary power ratio and supply coal con-
sumption rate are deeply reduced while electricity gen-
eration is increased when ID fan is driven by small tur-
bine. The proposed method is of great significance to
improve economic efficiency o f power plant and promote
the energy-saving process of thermal power units.
5. Acknowledgements
This study has been supported by the National Key
Technology R&D Program of China (2012BAC24
the Fundamental Research F
-sities (No. 11MG04) and th
Technology Cooperation Project (2010DFA 72760-609).
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